fix(forward): pair BW ACH ASCII reports using the _ASCII.TXT convention (v1.5.4)

Blastware's official Auto Call Home server writes per-event ASCII
reports as <stem>_<ext>_ASCII.TXT (e.g. N844L20G_630H_ASCII.TXT),
not <binary>.TXT (e.g. N844L20G.630H.TXT).  Versions v1.5.0–v1.5.3
only looked for the latter and silently shipped every binary alone,
so the SFM database lost the per-event Peak Acceleration / Peak
Displacement / ZC Freq / Time of Peak / Peak Vector Sum + time /
sensor self-check fields on every forwarded event.

Fix: pair-finding logic now tries the ACH-convention filename first
and falls back to <binary>.TXT for compatibility with operator-saved
manual exports and existing test fixtures.

  ach_report_name("M529LK44.AB0")    → "M529LK44_AB0_ASCII.TXT"
  legacy_report_name("M529LK44.AB0") → "M529LK44.AB0.TXT"

When both files exist (operator manually saved + ACH auto-exported),
ACH wins because that's the canonical name on modern BW deployments.
Both candidates checked case-insensitively against the cached
directory listing — no extra stat() calls.

6 new unit tests cover the new pairing logic, helper-function
correctness, and the precedence rule.  Total now 31 tests, all green.

Field-deploy note: re-running v1.5.4 on a folder where v1.5.0–v1.5.3
already ran will NOT re-forward historical events — the
sfm_forwarded.json state file remembers them by sha256.  To re-forward
historical events to populate SFM with the now-correctly-paired
reports, delete the state file before starting v1.5.4.

event_forwarder.py

@@ -96,9 +96,41 @@ def is_event_binary(path: str) -> bool:
     return True
 
 
+def ach_report_name(binary_name: str) -> str:
+    """BW ACH report-naming convention.
+
+    Blastware's official Auto Call Home server writes per-event ASCII
+    reports as ``<stem>_<ext>_ASCII.TXT`` — the ``.`` between stem and
+    ext is replaced with ``_`` and ``_ASCII.TXT`` is appended.
+
+    Examples:
+        ``M529LK44.AB0``  →  ``M529LK44_AB0_ASCII.TXT``
+        ``N844L20G.630H`` →  ``N844L20G_630H_ASCII.TXT``
+        ``H907L1R7.PG0H`` →  ``H907L1R7_PG0H_ASCII.TXT``
+
+    For a filename without a dot (defensive — shouldn't happen for real
+    BW events) we still append ``_ASCII.TXT``.
+    """
+    stem, dot, ext = binary_name.rpartition(".")
+    if not dot:
+        return binary_name + "_ASCII.TXT"
+    return stem + "_" + ext + "_ASCII.TXT"
+
+
+def legacy_report_name(binary_name: str) -> str:
+    """Manual-export convention: ``<binary>.TXT`` (e.g. when an operator
+    saves an event report to text directly from BW's UI rather than
+    letting ACH auto-export it).  Kept as a fallback so the codec-agent
+    test fixtures (``decode-re/5-8-26/event-c/M529LK44.AB0.TXT``) still
+    pair correctly."""
+    return binary_name + ".TXT"
+
+
 def report_path_for(binary_path: str) -> str:
-    """Return the conventional `<binary>.TXT` partner path."""
-    return binary_path + ".TXT"
+    """Legacy entry point — returns the manual-export path.  Prefer
+    :func:`ach_report_name` for new BW deployments.  Retained for
+    backward compatibility with any caller still on the old convention."""
+    return legacy_report_name(binary_path)
 
 
 def is_histogram_event(filename: str) -> bool:
@@ -109,9 +141,12 @@ def is_histogram_event(filename: str) -> bool:
     return False (the conservative answer — we don't want to suppress
     "no report" warnings on potentially-waveform old-firmware events).
 
-    Used purely for log clarity — histograms don't get auto-exported BW
-    ASCII reports, so "no report" on a histogram is not a problem to
-    flag.  Forwarding logic itself doesn't depend on this check.
+    Used purely for log clarity — when a forward goes through without a
+    paired TXT, the log distinguishes "histogram, no report expected"
+    (acceptable: BW may not have written one even though it normally
+    does for ACH-routed histograms) from "no report ⚠" on a waveform
+    (more suspicious: BW almost always writes the TXT for waveform events).
+    Forwarding logic itself doesn't depend on this check.
     """
     name = os.path.basename(filename)
     ext = os.path.splitext(name)[1].lstrip(".").upper()
@@ -314,12 +349,29 @@ def find_pending_events(
             skipped_already_forwarded += 1
             continue
 
-        # TXT pairing
-        txt_name = e.name + ".TXT"
-        # Case-insensitive match on the .TXT suffix
-        if txt_name not in names:
-            txt_name_lc = txt_name.lower()
-            txt_name = next((n for n in names if n.lower() == txt_name_lc), None)
+        # TXT pairing — try BW ACH convention first
+        # (<stem>_<ext>_ASCII.TXT) and fall back to the manual-export
+        # convention (<binary>.TXT).  Both checked case-insensitively
+        # against the cached directory listing.  ACH wins when both
+        # exist — that's the format BW's official ACH server writes.
+        candidates = [ach_report_name(e.name), legacy_report_name(e.name)]
+
+        # Case-insensitive name lookup against the cached set.
+        names_lc_to_actual = None
+        txt_name: Optional[str] = None
+        for cand in candidates:
+            if cand in names:
+                txt_name = cand
+                break
+            # Build lower-case index lazily — most folders have very few
+            # TXT files relative to binaries, so the linear scan only
+            # fires when neither exact-case candidate matches.
+            if names_lc_to_actual is None:
+                names_lc_to_actual = {n.lower(): n for n in names}
+            actual = names_lc_to_actual.get(cand.lower())
+            if actual:
+                txt_name = actual
+                break
 
         txt_path: Optional[str] = None
         if txt_name: